Membrane modules based on hollow fiber membranes or capillary membranes are used for the most varied purposes to filter or separate individual components out of a liquid or to add such components to liquids. Hollow fiber membranes as a rule have a semi-permeable wall with a porous structure via which the respective components permeate into the liquid or out of the liquid. In many cases, hollow fiber membranes are integrated in mats, such as e.g. woven or knitted mats for better processability as well as for the production of membrane modules with improved fluid dynamics. Mats of this type and multilayer wound bodies produced therefrom are described for example in U.S. Pat. No. 4,940,617 hereby incorporated by reference herein.
In the meantime, hollow fiber membrane modules have found broad use in the area of adding gases to liquids, degassing of liquids or in gas separation. Hollow fiber membrane modules, contactors, fabrics, or cartridges are described for example in U.S. Pat. No. 4,220,535, U.S. Pat. No. 5,186,832, U.S. Pat. No. 5,264,171, U.S. Pat. No. 5,284,584, and U.S. Pat. No. 5,352,361, each incorporated by reference herein.
In various processes in the pharmaceutical and chemical industries, it is necessary to run multi-step extraction processes, during which a dissolved component in an e.g. aqueous phase is initially extracted by means of an organic phase and this component is subsequently separated from the organic phase by means of a second aqueous phase. Multi-step processes of this type can be combined in a one-step process in membrane modules, which contain two groups of hollow fiber membranes, wherein the feed stream flows through the hollow fiber membranes of the one group and the stream finally containing the separated component (strip stream) flows through the hollow fiber membranes of the second group. The outer space around the hollow fiber membranes is filled with an extraction liquid, which transports the component to be extracted from the hollow fiber membranes of the first group to the hollow fiber membranes of the second group. Here, the liquid surrounding the hollow fiber membranes functions as a liquid membrane. Processes of this type are also described in the literature as CLM (contained liquid membrane) separation processes (see e.g. Majumdar et al., AlChE Journal, vol. 34 (1988), No. 7, pp. 1135-1145; Sengupta et al., AlChE Journal, vol. 34 (1988), No. 10, pp. 1698-1708; Basu et al., J. of Membrane Science, vol. 75 (1992), pp. 131-149). By means of these separation processes, components can be separated from liquid as well as from gaseous media. The membrane modules delineated in the literature cited have two groups of hollow fiber membranes which are arranged parallel to each other in the middle section of the housing.
In various applications in the area of CLM separation processes, the stability of the liquid phase, i.e. of the liquid membrane, is insufficient, and there exists a need for alternative module designs that enable a long-lasting stability of the liquid membrane.
An example for a membrane module design of this type or for a membrane contactor of this type with increased stability of the liquid phase is disclosed in U.S. patent application Ser. No. 12/112,071, filed on Apr. 30, 2008, published as US 2009/0272684 A1, published Nov. 5, 2009, hereby incorporated by reference herein. The CLM contactor described therein has a first and a second mat, composed of semi-permeable hollow fiber membranes which are arranged offset with respect to one another in the longitudinal direction of the hollow fiber membranes, said mats are wound around a perforated central tube. The ends of the hollow fiber membranes offset with respect to one another of the mats wound in this way into a hollow fiber membrane wound body are embedded at one end of the CLM contactor in a first and a third sealing compound and at the other end of the contactor in a second and a fourth sealing compound, wherein a first chamber is formed between the first and third sealing compounds as well as a second chamber between the second and fourth sealing compounds. Thereby, the walls of the hollow fiber membranes of the first hollow fiber membrane mat are fluid impermeable in the area of the first chamber and the walls of the hollow fiber membranes of the second hollow fiber membrane mat are fluid impermeable in the area of the second chamber, whereas the walls of the hollow fiber membranes are porous and semi-permeable outside of the respective chambers.